ArrayListを更新中に参照する

forでlistを読み込み中に、別スレッドでlist addすると
exceptionが発生する

class ReadTask implements Runnable {
    List<String> l;
    ReadTask(List l) {
        this.l = l;
    }
    @Override
    public void run() {
        try {
        for (String str:this.l) {
            System.out.println(str);
            try {
                Thread.sleep(1000);
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
        }
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}
class WriteTask implements Runnable {
    List<String> l;
    WriteTask(List l) {
        this.l = l;
    }
    @Override
    public void run() {
        for (int i=10; i<20; i++) {
            l.add(String.valueOf(i));
            System.out.println("added: " + i);
           try {
                Thread.sleep(1000);
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
        }
    }
}
public class Outer {
    public static void main(String[] args) {
        List<String> l = new ArrayList();
        l.add("1");
        l.add("2");
        l.add("3");
        ExecutorService es = Executors.newFixedThreadPool(3);
        es.submit(new WriteTask(l));
        es.submit(new ReadTask(l));
        es.shutdown();
    }
}

1
added: 10
2
added: 11
java.util.ConcurrentModificationException
	at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1043)
	at java.base/java.util.ArrayList$Itr.next(ArrayList.java:997)
	at com.mycompany.mavenproject1.ReadTask.run(Outer.java:21)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at java.base/java.lang.Thread.run(Thread.java:834)
added: 12
added: 13
added: 14
added: 15
added: 16
added: 17
added: 18
added: 19

CopyOnWriteArrayListに差し替えると、listのコピーを参照しに行く
結果exceptionが発生しない
コピーをとるタイミングはjvm次第？

List<String> l = new CopyOnWriteArrayList<>();

1
added: 10
2
added: 11
3
added: 12
10
added: 13
added: 14
added: 15
added: 16
added: 17
added: 18
added: 19